A spark plug is known, which includes: a metal shell fixed to an engine; a ground electrode having an electrode base coupled to the metal shell and a tip joined to the electrode base and containing a noble metal as a main component; and a center electrode insulatedly held in the metal shell. This spark plug generates, upon breaking of insulation between the center electrode and the ground electrode, spark discharge on a discharge path between the center electrode and the ground electrode. By the flow of air-fuel mixture in a combustion chamber of the engine, the discharge path is extended toward a downstream side of the air-fuel mixture flow. Thus, a spark wear region of the ground electrode increases in area with extension of the discharge path. Japanese Laid-Open Patent Publication No. 2004-152682 discloses a technique to cover the entire electrode base of the ground electrode, except a portion thereof to which the tip is joined, with a protection film of noble metal-based material for the purpose of improvement in spark wear resistance.